Study: Invasive mussels can survive in Tahoe's water

Quagga mussels can survive and possibly reproduce in Lake Tahoe, according to a new study that boosts concern over potential invasion of the famous alpine lake by the foreign mollusks.

"It's not good news," said Ted Thayer, natural resource and science team leader for the Tahoe Regional Planning Agency, which received the report last week from scientists at the University of Nevada, Reno and University of California, Davis.

The study suggests low calcium levels in Tahoe's waters, once hoped to act as a barrier against establishment of the mussels, may not offer sufficient protection after all.

"It appears that for adults, that's not the case. They are able to survive," said Sudeep Chandra, chief UNR researcher for the study. "The hypothesis we were testing is there would be no survival. I was quite surprised."

For the study, Chandra and colleagues removed eight quagga mussels from Lake Mead, where the mollusks were first discovered in January 2007. Trillions of mussels have since overrun the lake's ecosystem, displacing native invertebrates, experts said.

The mussels were transported to UNR, stored in tanks filled with Tahoe water and monitored over a 51-day period. All but one survived for a survival rate of more than 87 percent.

The mussels grew while in the Tahoe water, with 43 percent showing the potential for effective reproduction over that period, Chandra said. That was determined by examination of the mollusks' reproductive organs at the conclusion of the study period.

"At the age of reproduction they are able to survive. Eighty seven percent is fairly high," Chandra said.

"It doesn't look good so far," agreed co-researcher Marion Wittmann, an aquatic ecologist for the UC-Davis' Tahoe Environmental Research Center.

It is important to note the study did not examine survivability of mussels in their larval stage, a question Chandra and Wittmann said researchers should explore as soon as funding for more studies is secured. It is possible Tahoe lacks sufficient calcium to support juvenile mussels, they said.

"It's going to take a little more research to determine if this mussel can really sustain in populations over time," Wittmann said.

If established at Tahoe, quagga mussels or their cousin, zebra mussels, could cause profound changes to a sensitive ecosystem. The mussels could also clog water intakes, cover boats and piers and litter now pristine beaches with sharp and reeking shells.

One recent study by the U.S. Army Corps of Engineers estimates a mussel invasion could cost Tahoe's tourism economy more than $22 million per year.

"This could potentially be catastrophic for the lake," Thayer said. "This is disappointing. It would have been nice if it had come back that there wasn't that high a risk."

TRPA and other agencies have taken steps over the last two years to prevent introduction of the mussels, including inspection of all boats launching into the lake. Recreational boats with hitchhiking mussels attached are believed to pose the greatest risk for bringing mussels to the lake.

Officials are now considering moving those inspections from boat launches to larger stations in various places around the lake, a change that will help avoid long lines and allow for more thorough decontamination of those vessels deemed to be a risk. In the more distant future, TRPA could chose to inspect vessels at highway entry points to the Tahoe Basin, Thayer said.

While the latest study underscores the potential danger to Tahoe posed by quagga and zebra mussels, Chandra said he believes an aggressive program to keep mussels out of the lake can be effective. Tahoe is by no means doomed to infestation, he said.

"When you reduce the likelihood of transfer, almost always those ecosystems are protected," Chandra said. "Using sound science and good policy, the lake can be protected."